1. Field of the Invention
Embodiments of the present invention generally relate to a valve assembly for selectively blocking or redirecting flow. More particularly, embodiments of the invention relate to a valve assembly having a gate that compensates for misalignment with a seat of the valve assembly.
2. Description of the Related Art
Industrial valves have many uses for selectively blocking or redirecting a flow of fluids such as gases and liquids, solids and mixtures thereof. Examples of industries that commonly utilize valves include water utilities, power plants, refineries and chemical manufacturing. Open/close type valves may be used to selectively block flow through a conduit. On the other hand, diverter type valves effectively block flow through one passageway of the valve and open flow through a diverted passageway of the valve depending upon the position of the valve. These diverter valves have particular utility in permitting isolation of one line due to, for example, an emergency condition such as a line rupture or construction on a portion of the line that is blocked by the valve while permitting flow though another line such as a bypass.
One type of valve which may be referred to as a “flapper valve” utilizes a gate or disc that pivots about one end thereof in order to permit a face of the disc to make positive contact to a valve seat within the valve. In the open position, the disc is rotated (e.g., 90°) such that the plane of the disc is substantially axially aligned with a flow of fluid through the valve and does not substantially interfere with the fluid flow. Rotation of the disc toward the valve seat closes the valve to fluid flow once the disc makes contact with the valve seat. Contact between the disc and the valve seat may form a seal to completely prevent fluid flow through the valve.
A variation of the flapper valve may be configured as a diverter valve which may be referred to as a “flip-flop diverter valve.” A disc of the flip-flop diverter valve can rotate between a first position and a second position. The disc contacts a first seat along a first fluid passageway of the valve when in the first position and contacts a second seat along a second fluid passageway when in the second position. Thus, the flip-flop diverter valve operates similar to the flapper valve to selectively block fluid flow through the first passageway of the valve and thereby open fluid flow through the second fluid passageway.
Proper sealing between the disc and the valve seat requires that the disc be properly aligned with respect to the valve seat such that the entire perimeter of the disc tightly contacts the valve seat when closed. Even if manufactured with a correct initial alignment, the alignment between the valve seat and the disc can change due to possible movements of the valve seat, thereby causing a loose contact between the disc and the valve seat that may prevent proper sealing. For example, temperature changes of the valve can cause expansion or contraction of the valve or valve seat itself, which may cause the surface of the valve seat that the disc contacts to move relative to the disc fixed within the valve. In the case where the valve seat includes a cone within the valve, the cone grows as the temperature rises such that the valve seat and disc may not be properly aligned due to the reduced spacing therebetween. Manufacturing a predetermined alignment between the disc and the valve seat in order to compensate for the movements still only accommodates the valve seat at one particular location and fails to account for applications of the valve having various temperatures and for the inability to determine the exact temperature of operation and amount of movement of the valve seat.
Therefore, there exists a need for a valve assembly having a gate or disc that compensates for misalignment with a valve seat when rotated into contact therewith. There exists a further need for a diverter valve having a gate or disc that rotates between two valve seats and that compensates for misalignments between the valve seats and the gate.